1. Field of the Invention
The present invention relates generally to the field of material mixing methods and apparatus, and more particularly to a dynamic delivery line mixing method and apparatus for actively agitating a feedstock while the feedstock is being passed to a discharge device through a delivery conduit.
While the present invention is subject to a wide range of mixing applications, it is particularly well suited for suspending solids in liquids within the delivery lines of various spray systems, such as sophisticated spray paint systems and coating systems designed for either manual or robotic operation.
2. Technical Background
The vast majority of spray application, fluid processing, and other feedstock delivery systems incorporate one or more fluid delivery conduits through which a feedstock, in liquid, gaseous, or solid form, to include combinations thereof, travels en route to an applicator or other delivery device, such as a spray nozzle, or burner assembly. A common shortcoming associated with such systems is the formation of blockages, either partial or complete, in the delivery conduit. In the case of feedstocks that include solids suspended in a liquid, a contributing factor to these blockages is the separation of the solids from the liquid suspension.
For spray systems such as spray painting systems and spray coating systems used for applying specialty paints and coatings to machines and devices manufactured for specialized government entities such as, but not limited to, the Department of Defense and NASA, this shortcoming is particularly problematic. Typically, the paints and coatings used in such applications are considered highly loaded, in that heavy solids such as metals are suspended in a liquid feedstock to form the paint or coating prior to entering the delivery conduit. Due to the weight of such metals and other solid materials, separation or settling of the solid from the liquid within standard delivery conduits is a common occurrence. The rate at which such solids settle out of suspension depends upon such factors as the rate of delivery of the feedstock to the application device, the weight of the metals, the amount of time the feedstock remains stationary within the line between applications, the length of the delivery conduit, and the number of bends or turns encountered by the feedstock as it passes through the delivery conduit. The slower the delivery, the heavier the metal, the longer the application process is idle, the longer the length of the conduit, and the greater the number and magnitude of the bends, the greater the rate of settling. Even when the feedstock is moving through the conduit, it is essentially moving in one direction, thus, in standard delivery conduits vertical components of force counteracting the force of gravity on these metals are essentially non-existent. Accordingly, even if the feedstock is rapidly forced through the delivery conduit, a significant quantity of solids will settle to the bottom of the conduit over time.
Such setting, over time, results in significant blockages within the delivery conduit, which in turn reduce the efficiency of the spray system being employed. Additionally, many of today's sophisticated computer controlled spray systems are designed to apply paints or coatings at precise rates. When a partial blockage in the delivery line occurs, the systems typically compensate for the reduced flow rate due to the decreased diameter of the conduit by increasing the flow, typically by increasing pressure. Providing this increased flow requires the drive mechanisms to work in excess of their normal operating parameters which often results in undue wear and tear on the drive mechanism, and in certain instances, unexpected failure of the drive mechanism. Moreover, as portions of any such blockages break away from the walls of the delivery conduit, they often become lodged in the reduced diameter orifices of the spray nozzles or jets of the sprayers themselves. The blockages occurring due to the use of standard delivery conduits thus necessitate frequent cleaning of the spray systems which in turn results in increased system down time and business interruption.
In addition, many of the metals and solids delivered in suspension for Department of Defense projects are highly specialized and proprietary in nature. Accordingly, these solids often cost $500.00 or more per quart. Together, the economic loss resulting from frequent cleaning of the delivery systems and significant loss of the solids resulting from cleaning operations often result in lost profits to the system owners, or increased costs to the customers, or both.
In an attempt to overcome these and other shortcomings, systems users have generally taken one of two approaches. One approach is the incorporation of a recirculation pump with present systems. Typically, the recirculation pump is connected to the standard delivery conduit at one or more low points or turns in the delivery line. As solids collect in these low points or turns in the delivery conduit, the recirculation pump is selectively engaged to drain the solids from the delivery conduit and recirculate them back to the supply vessel or pressure pots used to suspend the solids and the liquids prior to the suspension being delivered into the delivery conduit. Such storage vessels or pressure pots typically incorporate a paddle or other mixing device which continuously moves within the vessel to uniformly mix the feedstock. In theory, the solid material returned to the storage vessel via the recirculation pump should maintain the system at equilibrium. However, equilibrium is rarely obtained as the recirculation pump itself becomes a collection site for solid deposits. In addition, the pump components suffer undue wear and tear due to continuous contact with the heavy solid and thus require frequent repair and replacement parts. Moreover, such recirculation systems are often cost prohibitive for the benefits they provide.
The second way systems users have attempted to mitigate against delivery conduit blockages is through the use of static mixers (also known as motionless mixers to those skilled in the art). Static mixers are typically positioned immediately before the delivery conduit or partially within the end of the delivery conduit remote from the application device. Such mixers are typically rigid structures having a plurality of angled surfaces, and are designed to break up the flow of the feedstock as it enters the delivery conduit. As a result of being static, however, the plurality of surfaces of these static mixers themselves become prime collection points for the heavy solids. As a result, the static mixers themselves often promote blockage of the delivery conduits.
In view of the foregoing, there is a need for an apparatus and method for mixing one or more feedstocks within the delivery conduit of feedstock delivery systems such as sophisticated spray paint and coating systems. In addition, there is a need for an apparatus and method that maintains a majority of heavy solids in suspension within the feedstock while the feedstock is passed through the delivery conduits of spray systems and the like. Such a device should be simple to use, inexpensive to manufacture and maintain, and substantially impervious to the substances to which it will be exposed within the delivery conduit. It is to the provision of such a device and method that the present invention is primarily directed.